1. Field of the Invention
The present invention relates to a pressure control valve which controls a refrigerant pressure at an outlet side of a radiator based on a refrigerant temperature at the outlet side of the radiator, and it is preferably applicable to a vapor compression type refrigeration cycle in which carbon dioxide (CO.sub.2) is used as a refrigerant.
2. Description of Related Art
Hitherto, there has been known means for attempting to improve a refrigeration performance by means of lowering enthalpy of the refrigerant at an inlet side of an evaporator by performing heat exchange between the refrigerant at an outlet side of the evaporator and that at the outlet side of the radiator.
Furthermore, as a control valve for adjusting a valve port based on the refrigerant temperature at the outlet side of the radiator, there has been known an invention disclosed in Japanese Patent Application Laid-Open No. Shou 55-54777.
According to the control valve disclosed in the above prior art, since a temperature sensing portion for sensing the refrigerant temperature at the outlet side of the radiator and the valve port whose opening degree is to be adjusted according to an internal pressure of the temperature sensing portion are provided in the same flow passage in series, there is a problem that the refrigeration performance cannot be improved by the aforementioned means.
In order to solve this problem, as disclosed in Japanese Patent Application Laid-Open No. Hei 5-203291, there is considered means in which the temperature sensing portion is made into a temperature sensing cylinder using a capillary tube to detect the refrigerant temperature at the outlet side of the radiator. However, in this means, since a heat sensed by the temperature sensing cylinder transmits to a control chamber at a diaphragm side through the capillary tube, the temperature change in the control chamber is lagged with respect to a refrigerant temperature change at the outlet side of the radiator. Therefore, by this means, a response characteristic of the control valve with respect to the refrigerant temperature change at the outlet side of the radiator (hereafter, this response characteristic is referred to as temperature response characteristic) is compromised, so that it is impossible to suitably control the refrigeration cycle.
Further, since it is necessary to assemble the capillary tube and the temperature sensing cylinder to the outlet side of the radiator, the manufacturing processes for the refrigeration cycle is increased.